1. Field of the Invention
The present invention generally relates to a power generating device and, more particularly, to a wind power system capable of transforming a varying rotation speed into a constant rotation speed.
2. Description of the Prior Art
The wind turbine is a power transforming system capable of transforming wind power into mechanical power and then mechanical power into electrical power. Nowadays, all the large wind turbines are grid-tied so that the power generated by the wind turbines can be fed into the grid. However, the power of the grid has a constant frequency and a constant voltage. Therefore, there must be a certain apparatus for transforming the varying frequency power into the constant frequency power.
In JP2004162652A (2004) as shown in FIG. 1, a rotor 10 transmits the power to the electric generator 11 through two transmission paths 101 and 102. In the first transmission path 101, gear sets 12 and 13 and gear sets 14 and 15 are used to transmit the power to an internal gear of the planetary gear set. In the second transmission path 102, the torque and rotation speed are controlled by a continuously variable transmission (CVT) mechanism and part of the power from the rotor is transmitted to a planet carrier of the planetary gear set through gear sets 16 and 17 and gear sets 18 and 19. The planetary gear set is a differential gear train, wherein the internal gear and the planet carrier are the inputs. The sun gear 111 outputs the power to the electric generator 11. This disclosure is characterized in that the output rotation speed of the continuously variable transmission (CVT) mechanism is controlled and the differential gear train is used to keep the rotation speed of the electric generator as a constant.
In US2005146141A1 (DE10357292) filed by Voith in 2005 as shown in FIG. 2, the planetary gear set is a differential gear train. Two transmission paths are used to keep the rotation speed of the electric generator as a constant. First, the rotation speed of a rotor 20 is increased by a main gear box 21 and the rotor 20 transmits the power to a planet carrier of the differential gear train. A sun gear shaft 22 is used as an output shaft of the differential gear train to transmit the main power to the electric generator 23. The torque and rotation speed are controlled by a hydraulic torque converter 24, then the other power is transmitted to the internal gear of the differential gear train through the gear set 25. The output speed of the differential gear train is controlled as a constant, so that the rotation speed of the electric generator is kept as a constant. The torsional vibration and load fluctuation are eliminated by liquid damping of the hydraulic torque converter. These increase the compatibility between the wind turbine and the grid and reduce the load acting on other devices. However, the hydraulic torque converter is sensitive to temperature variation and has low efficiency at low rotation speed.
In U.S. Pat. No. 4,774,855A1 (1988) as shown in FIG. 3, hydraulic static transmission and planetary differential gear train are used to perform speed control. The rotation speed of a rotor 30 is increased by a main gear box. The power is divided into two parts. Part of the power is transmitted to a planet carrier in the differential gear train through gear sets 31 and 32, while another part of the power is transmitted to a sun gear 39 of the differential gear train through gear sets 31 and 33, a hydraulic pump 34, hydraulic pipelines 35, a hydraulic motor 36, and gear sets 37 and 38. The differential gear train performs a speed control so that the internal gear can output with constant rotation speed. However, hydraulic static transmission is sensitive to temperature variation and has low efficiency at a low rotation speed, otherwise, the phenomenon of nonlinear for hydraulic static transmission must be considered.